50 mL of a gaseous hydrocarbon is mixed with excess of oxygen and burnt and cooled to the laboratory temperature. The reduction in volume was found to be 150 mL. The gas is then passed into caustic potash, when there is a further reduction in the volume of 150 mL. Provide all the volumes are measured at the same conditions of temperature and pressure, find out the molecular formula of the hydrocarbon.

Explanation

Chemical reaction equation to combustion reaction is
`{:(C_(x)H_(y)+O_(2) to CO_(2)+H_(2)O),("50mL"" 150mL"" 150mL"):}`
We know volume of gas has same number of moles, at same temperature and pressure
`{:("50 moles"" 150 moles"" 150 moles"),(C_(x)H_(y)+(x+y/4)O_(2) toxCO_(2) + y/2 H_(2)O),("50 mole"" 150 mole"" 150 mole"):}`
Given that reduction in volume, when the gases mixture is cooled to the laboratory temperature = 150 mL
`:. y/2 (50) = 150 rArr y = 6`.
and `x (50) = 150 rArr x = 3`
`:.` Hydrocarbon is `C_(3)H_(6)`.